The present invention relates to a fluid friction clutch which is controlled as a function of temperature and rotational speed, and to a fluid friction clutch controlled solely as a function of rational speed. In clutches of this type, a driving primary member and a driven secondary member are provided, between which is situated a working chamber for containing a viscous fluid. The primary member is further provided with a reservoir chamber such that a fluid connection is provided, which is controllable with respect to the degree of its opening.
Fluid friction clutches of this general type are known from German Offenlegungsschrift No. 24 39 256. This known type of clutch has several disadvantages. It has a relatively deep dimension in the axial direction as a result of the cylindrical working surfaces; the superposition of the effects of temperature and rational speed on one control element leads to an inadequate control behavior of the clutch; and because of the fastening of the control element to the primary member, a relative movement between the valve lever and the actuating pin occurs which is accompanied by undesirable friction.